Optical fibre communication systems and optical fibre based instruments and devices often require the accurate alignment and reliable attachment of optical fibres with integrated optical devices such as waveguides integrated on a substrate. One important consideration in the design of such optical connections is that good alignment is achieved between the waveguide and the optical fibre. A typical structure of such an optical connection is that of a fibre set within a V-groove to a waveguide integrated on a silicon substrate. Such a structure based on silicon rib or ridge waveguides integrated on silicon insulator wafer is described in PCT GB96/01068. In order to achieve a good connection, the fibre should be brought to within a gap of 5.mu.m or less of the waveguide facet. Since the V-groove does not have an end face perpendicular to the base of the groove, but rather it is set at an angle towards the base, it is desirable to undercut the waveguide to form a waveguide structure overhanging the angled face like a "diving board". Such a concept can be found in PCT/GB96/01068. Whilst this particular concept is a desirable way of achieving the appropriate alignment features, processing tolerances can cause the overhanging structure to exhibit an unwanted "shelf" of buried oxide extending beyond the end facet of the waveguide after the V-groove has been formed. When a nitride layer is deposited over the end face containing the oxide shelf, a small nitride "shelf" can likewise be formed. If left, the shelves would distort the exit of optical waves from the waveguide. It is an aim of this invention to improve the surface quality of the waveguide facet to provide an improved optical connection to an optical fibre.